An optical encoder is a position sensor for measuring the rotation angles or the movement distances of a subject. Known optical encoders include transmission-type encoders in which light that has passed through the slits provided in the encoder disc is detected by a light receiving element to perform positioning, and reflection-type encoders in which reflection regions and non-reflection regions are provided on the encoder disc, and light that have been reflected from the reflection regions are detected by a light receiving element to perform positioning.
For example, Japanese Patent Application Publication No. 2007-121142 discloses a reflection-type encoder disc (a reflection plate for an optical encoder) including: an optical disc; an absorption layer formed on a surface of the optical disc; and a reflection layer patterned on a surface of the absorption layer. Typically, a conventional reflection plate for an optical encoder in which a patterned reflection layer is arranged on the surface of a non-reflection layer is manufactured by the following method. That is as shown in FIGS. 13A to 13F, a non-reflection layer 25 is first formed on a base material 21 by vacuum evaporation, sputtering, or the like (FIG. 13A). Thereon, a reflection layer 26 is formed by vacuum evaporation, sputtering, or the like (FIG. 13B). Subsequently, after funning a photoresist film 22 on the reflection layer 26 (FIG. 13C), the photoresist film 22 is subjected to exposure via a photomask. The photoresist film 22 after exposure is subjected to development to form a resist pattern 22a (FIG. 13D). With the resist pattern 22a used as a mask, the reflection layer 26 is subjected to etching or the like to expose the non-reflection layer 25 (FIG. 13E). After that, the resist pattern 22a is removed to expose the patterned reflection layer 26 (FIG. 13F). As a result, a conventional reflection plate for an optical encoder whose surface has non-reflection regions and patterned reflection regions is obtained.
In manufacturing a reflection plate, such as a conventional reflection plate for an optical encoder, having a non-reflection layer and a reflection layer arranged thereon, each layer is typically deposited by a vacuum process such as vacuum evaporation, sputtering, or the like. However, typically, vacuum evaporation apparatuses are comparatively expensive, and require a comparatively high equipment cost. Furthermore, there is a possibility that, in some types of non-reflection layers and reflection layers, exfoliation is produced due to a stain or a scratch on the surface of the layer.